With any internal combustion engine it is desirable to treat the exhaust gases so that they can be safely discharged into the atmosphere. In some engines, particularly the diesel type, one of the operating problems is the presence of solid particles which are carried in the exhaust gas stream.
The particles are normally comprised of bits of carbon. They result from the incomplete combustion of the hydrocarbon fuel mixture under particular operating conditions. However, the operating efficiency of the engine is also a contributing factor to the amount of carbon produced.
The presence of relatively large amounts of carbon particles in any exhaust gas stream is evidenced by a dark, smoky, undesirable effluent. Such smoke is not only offensive to the smell; it can also be undesirable to the environment.
Means have been provided and are known in the prior art, for the elimination, or minimization of the carbon content in exhaust discharge streams. It has been found, for example, that most carbon particles can be eliminated by a suitable filter of proper construction. Eventually, however, the latter can become saturated and/or inoperable due to excessive carbon accumulations.
It should be appreciated that accumulation of carbon particles is prevalent under all diesel engine operating conditions. It is further appreciated that the quantity and quality of an exhaust gas stream created in any internal combustion engine will vary in accordance with the operating characteristics of the engine. For one thing the temperature range experienced by the diesel exhaust gas stream can vary between slightly above ambient air temperature, and temperatures in excess of 1200.degree. F.
Where it is found that an engine continuously operates under such circumstances that carbon is continuously produced and accumulated in the filter, the latter must occasionally be rejuvenated. Under usual engine operating conditions, carbon in the exhaust gas stream as well as any accumulated carbon will be burned off by contact with exhaust gas in excess of 900.degree. F. More precisely, hot exhaust gas will initiate carbon combustion, and the oxygen content of the gas will support the combustion event.
The combustion of any large, and contained carbon accumulation can produce temperatures greatly in excess of the exhaust gas temperature. The result is that at excessive temperatures the filter is susceptible to thermal damage. The latter can be a minor distortion of the bed structure or it can be a major deformation thereof.
Toward achieving a satisfactory or controlled rate of carbon removal from an exhaust gas system without resulting damage to the filter, the unit presently disclosed is provided. The instant filter thus comprises in brief, a reaction chamber through which a hot stream of carbon particle carrying exhaust gas is passed.
During engine operating conditions when the exhaust gas is at a relatively low temperature, such as start-up from cold, the greatest amount of carbon particles will be carried into the filter bed. Heavy carbon deposits will also result from operation under heavy load conditions. In either instance, the exhaust gas stream is introduced to the filter reaction chamber and passed through at least one filter bed.
Within the bed, combustion of the carbon particles is initiated upon contact with the hot exhaust gas. Combustion in the bed is further maintained by the combustion supporting component, particularly oxygen, contained in the exhaust gas. In brief, the greater the oxygen content of the hot incoming gas, the hotter and more rapid will be the burning event within the bed.
Without any restraint on the rate of burning within the bed the latter could, as noted, suffer damage. More particularly, depending on the composition of the bed, the temperature could reach a point where it will cause the bed to be distorted, fractured, or otherwise rendered less efficient than it should be.
To control the rate of burning in the filter bed the flow of combustion supporting gas to the latter is regulated. Thus, the incoming particle carrying gas is supplemented with a stream of gas taken from the filter outlet port. The effect of the gas mixing is that exhaust gas from the engine, which is relatively rich in oxygen, will be intermixed with treated exhaust gas which has been substantially depleted of oxygen by the burning within the filter bed. Thus, with the reduced amount of oxygen present, the further burning of the carbon particles will be at a much slower rate. This will lessen the opportunity for the bed structure to be thermally damaged.
It is therefore an object of the invention to provide a method for operating an internal combustion engine wherein the hot exhaust gas is treated to remove solid matter. Another object is to provide a filter member for an internal combustion engine which is capable of being safely rejuvenated by removal of carbon from the filter bed. A further object is to provide a filter of the type disclosed wherein burning of carbon within the filter structure is controlled by regulation of the combustion supporting element which is passed through the filter. A still further object is to provide an exhaust system of the type contemplated wherein an exhaust filter is periodically treated to remove carbon, and the burning of the latter is controlled by intermixing of particle carrying exhaust gas with a stream of non-combustion supporting gas. In the preferred practice of the invention, a hot, particle containing exhaust gas stream is passed through a particle retaining bed. In the latter, at least a part of the contained particles are removed by retention on the filter bed walls and passages.
Hot exhaust gas is introduced to the bed to burn the retained particles. However, the rate of such combustion is regulated by varying the composition of exhaust gas entering the bed.
Said exhaust gas thus comprises a mixture of hot gas from the engine, which is mixed with treated exhaust. The latter is in a condition of being substantially free of carbon particles as well as combustion supporting gas such as oxygen.